1. Field of the Invention
This invention relates to an improved marine impeller type propulsion unit which operates under water for motion control of a marine vessel in multiple degrees of freedom.
2. Description of the Prior Art
Most marine craft presently are propelled and controlled by single fixed propulsion devices such as screws and control surfaces. This limits the placement of shipboard internal propulsor machinery that drives the propeller and requires additional drag producing motion control appendages such as rudders and diving planes. Other marine crafts use alternate mechanical propulsors that change a propeller's cyclic and collective blade pitch that in turn generates thrust vectors to produce up to three degrees of freedom (up/down, right/ left, forward/reverse). U.S. Pat. No. 3,101,066 issued to Haselton, et al., for example, discloses a propulsor unit which uses a swash plate for the pitch control mechanism. This type of propulsors are used as ship secondary propulsors that use Voith-Schneider propeller (vertical axis propeller) and underwater submersibles. Particular means of mechanically varying the propeller blade pitch includes a swash plate ring that floats on rubber or steel spring mounts to permit freedom of movement when actuators push and/or pull the ring along the axis of rotation and when the ring is angled to the axis of rotation.
Limitations and disadvantages of the system disclosed in U.S. Pat. No. 3,101,066 include: (1) "lacking durability" and exhibiting "much lost motion", as described in Hazelton's later U.S. Pat. No. 3,450,083; (2) limited use to tandem propeller type propulsion configuration that precludes its use on other marine vessels such as a surface vessel; (3) the ring on a propulsion motor as shown does not incorporate both the swash plate control mechanism and actuator means in the central bore section of the motor that makes for an integral propulsion unit; and (4) the floating swash plate ring requires a large open bore structure for its placement which induces lost motion.
U.S. Pat. No. 3,450,083 discloses an improvement of the system described in U.S. Pat. No. 3,101,066. It discloses an improved way of supporting the swash plate ring which controls the cyclic and collective pitch of the propellers with an internal ring gear drive mechanism. Limitations and disadvantages of this system include: (1) the use of rotating seals in the drive motors to prevent leakage; (2) the need for a conventional in-line motor for driving the hull gear drive unit, thus requiring more internal marine vessel space; and (3) limited to use in a tandem propeller type propulsion configuration that precludes its use on other marine vessels such as a surface vessel.
Other propulsion units include Kawasaki Heavy Industries's Varivec propeller unit which consists of a swash plate, that is actuated by servo-actuators, which alters each propeller blade's combined cyclic and collective pitch that can generate thrust in any direction. Limitations and disadvantages of this unit include: (1) the need for a rotating shaft seal on the electric motor; and (2) an in-line electronic motor/speed reducer unit that requires more internal vessel space, thus limiting the flexibility for drive unit placement on a marine vessel.
U.S. Pat. No. 5,028,2I0 issued to Peterson, et al., describes an improved marine impeller type propulsion unit, the disclosure of which is incorporated herein by reference. U.S. Pat. No. 5,028,210 discloses a marine propulsion unit secured to an exterior of a marine hull, which is driven by a ring shaped prime mover defining a central bore section with a central axis. A plurality of propulsion blades radially extend from a hub which rotates about the central axis. Each of the blades is independently capable of pivotal movement, whereby the pitch angle thereof is adjusted selectively to provide pitch, yaw and fore/aft motion to the hull. A swash plate mechanism is mounted within the hub and to an inner central axle which is concentrically situated with the hub to control the blade pitch, collectively and cyclically, during the rotation of the hub. The swash plate mechanism is securely supported by an axially movable cylindrical support bearing which is connected to the central axle. A plurality of actuators are disposed within the central bore and around the central axle and are attached to the swash plate mechanism. By simultaneously actuating all the actuators in the same direction, the entire swash plate can be moved in the axial direction about the cylindrical support bearing to collectively change the pitch of the blades. On the other hand, to cyclically change the pitch of the blades, only some or all are actuated in different directions to tilt the swash plate in the desired direction.
In U.S. Pat. No. 5,028,210, the propeller shaft which drives the hub is equipped with a channel which engages a first scissor bearing located at the perimeter of the swash plate to rotate the swash plate about a water lubricated U-shaped bearing housed in the bearing pad which in turn is supported on the cylindrical support bearing. A second scissor bearing is operatively connected to the bearing pad to prevent rotation of the bearing pad caused by the frictional drag of the swash plate. While the second scissor bearing is supported so as to prevent a rotational movement about the cylindrical support bearing, it permits movement in the axial direction. This allows the link arm, which is used to rotate the blade, without having to carry the rotational load.